The present invention generally relates to papermaking belts useful in papermaking machines for making strong, soft, absorbent paper products. More particularly, the invention relates to papermaking belts comprising a resinous framework and a reinforcing structure joined thereto.
Generally, a papermaking process includes several steps. Typically, an aqueous slurry of papermaking fibers is formed into an embryonic web on a foraminous member, such, for example, as a Fourdrinier wire. After the initial forming of the paper web on the Fourdrinier wire, or forming wires, the paper web is carried through a drying process or processes on another piece of papermaking clothing in the form of endless belt which is often different from the Fourdrinier wire or forming wires. This other clothing is commonly referred to as a drying fabric or belt. While the web is on the drying belt, the drying or dewatering process can involve vacuum dewatering, drying by blowing heated air through the web, a mechanical processing, or a combination thereof.
In through-air-drying processes developed and commercialized by the present assignee, the drying fabric may comprise a so-called deflection member having a macroscopically monoplanar, continuous, and preferably patterned and non-random network surface which defines a plurality of discrete, isolated from one another deflection conduits. Alternatively, the deflection member may comprise a plurality of discrete protuberances isolated from one another by a substantially continuous deflection conduit, or be semi-continuous. The embryonic web is associated with the deflection member. During the papermaking process, the papermaking fibers in the web are deflected into the deflection conduits and water is removed from the web through the deflection conduits. The web then is dried and can be foreshortened, by, for example, creping. Deflection of the fibers into the deflection conduits of the papermaking belt can be induced by, for example, the application of differential fluid pressure to the embryonic paper web. One preferred method of applying differential pressure is exposing the web to a fluid pressure differential through the drying fabric comprising the deflection member.
Through-air-dried paper webs may be made according to any commonly assigned and incorporated herein by reference U.S. Pat. Nos. 4,529,480 issued to Trokhan on Jul. 16, 1985; 4,637,859 issued to Trokhan on Jan. 20, 1987; 5,364,504, issued to Smurkoski et al. on Nov. 15, 1994; 5,529,664, issued to Trokhan et al. on Jun. 25, 1996; and 5,679,222, issued to Rasch et al. on Oct. 21, 1997.
Generally, a method of making the deflection member comprises applying a coating of liquid photosensitive resin to a surface of a foraminous element, controlling the thickness of the coating to a pre-selected value, exposing the coating of the liquid photosensitive resin to light in an activating wave-length through a mask, thereby preventing or reducing curing of selected portions of the photosensitive resin. Then the uncured portions of the photosensitive resin are typically washed away by showers. Several commonly assigned U.S. Patents which are incorporated herein by reference, disclose papermaking belts and methods of making the belts: U.S. Pat. Nos. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; 4,528,239, issued Jul. 9, 1985 to Trokhan; 5,098,522, issued Mar. 24, 1992; 5,260,171, issued Nov. 9, 1993 to Smurkoski et al.; 5,275,700, issued Jan. 4, 1994 to Trokhan; 5,328,565, issued Jul. 12, 1994 to Rasch et al.; 5,334,289, issued Aug. 2, 1994 to Trokhan et al.; 5,431,786, issued Jul. 11, 1995 to Rasch et al.; 5,496,624, issued Mar. 5, 1996 to Stelljes, Jr. et al.; 5,500,277, issued Mar. 19, 1996 to Trokhan et al.; 5,514,523, issued May 7, 1996 to Trokhan et al.; 5,554,467, issued Sep. 10, 1996, to Trokhan et al.; 5,566,724, issued Oct. 25, 1996 to Trokhan et al.; 5,624,790, issued Apr. 29, 1997 to Trokhan et al.; 5,628,876 issued May 13, 1997 to Ayers et al.; 5,679,222 issued Oct. 21, 1997 to Rasch et al.; and 5,714,041 issued Feb. 3, 1998 to Ayers et al., the disclosures of which are incorporated herein by reference.
While curing of the photosensitive resin has proved to be an effective way of making the papermaking belt, a search for improved methods and products has continued. Now, it is believed that the deflection member may be made by at least several other methods which do not necessarily require the use of the curing radiation.
Accordingly, the present invention provides a novel process for making a papermaking belt by first, forming a desired pattern of a fluid resinous material in a molding member, and then transferring the resinous material from the molding member to the reinforcing structure and solidifying the patterned resinous material. The present invention also provides a process wherein the transferal of the resinous material from the molding member to the reinforcing structure is assisted by application of fluid pressure differential. The present invention also provides a process that reduces the amount of the resinous material required to construct the papermaking belt comprising a reinforcing structure and a patterned resinous framework. The present invention also provides an apparatus comprising a molding member for forming a desirable pattern of the resinous material and subsequently transferring the patterned resinous material to the reinforcing structure of the belt being constructed.
These and other objects of the present invention will be more readily apparent when considered in reference to the following description, in conjunction with the accompanying drawings.
A papermaking belt that can be made by a process and an apparatus of the present invention comprises a reinforcing structure and a patterned resinous framework joined thereto. The reinforcing structure has a first side and an opposite second side. Preferably, but not necessarily, the reinforcing structure comprises a fluid-permeable element, such as, for example, a woven fabric or a screen having a plurality of open areas therethrough. The reinforcing structure may also comprise a felt. The resinous framework has a top side and a bottom side, the top and bottom sides corresponding to the first and second sides of the reinforcing structure, respectively. The resinous framework may have a substantially continuous pattern, a discrete pattern, or a semi-continuous pattern.
A process for making a papermaking belt comprising a reinforcing structure and a resinous framework joined thereto includes the following steps: providing a reinforcing structure having a first side, a second side opposite to the first side, and a thickness formed therebetween; providing a flowable resinous material; providing an at least partially fluid-permeable molding member; depositing the flowable resinous material onto or into the molding member, preferably in a pre-selected pattern; juxtaposing the reinforcing structure with the molding member; applying a fluid pressure differential to the flowable resinous material associated with the molding member thereby transferring the flowable resinous material from the molding member to the reinforcing structure, preferably substantially in the pre-selected pattern, and causing the flowable resinous material and the reinforcing structure to join together; and solidifying the resinous material thereby forming the resinous framework joined to the reinforcing structure.
Preferably, the process further comprises a step of pre-solidifying the flowable resinous material prior to the step of applying a fluid pressure differential such that the resinous material reaches a condition in which it can sufficiently retain a desired shape during the step of applying the fluid pressure differential. The flowable resinous material preferably penetrates into the thickness of the reinforcing structure. Preferably such penetration occurs during the step of applying the fluid pressure differential and is sufficient for the resinous material to effectively join the reinforcing structure by locking on individual elements thereof. The apparatus of the present invention preferably comprises a means for pre-solidifying and/or solidifying the flowable resinous material, which means depends on the nature of the resinous material
The step of depositing the flowable resinous material onto or into the molding member preferably comprises contacting the molding member with the flowable resinous material and then removing excess of the flowable resinous material from the molding member. Any means known in the art may be used to deposit the flowable resinous material onto or into the molding member. The examples include: a trough, a spray, an extruder. Preferably, the flowable resinous material is deposited onto or into the molding member in a pre-selected pattern.
The molding member has a molding surface preferably comprising a plurality of fluid-permeable molding pockets structured to receive the flowable resinous material therein. The molding pockets may form a substantially continuous pattern, a pattern of discrete molding pockets, or a semi-continuous pattern. In some embodiments, at least some of the molding pockets may have differential depths. The molding member may further comprise a pattern of recesses for receiving the reinforcing structure therein. In one embodiment, the molding member comprises a molding roll having a circumference and a longitudinal axis perpendicular to the machine direction, the molding roll being rotatable about its longitudinal axis. In another embodiment, the molding member comprises at least one endless band structured and designed to continuously travel in a pre-determined direction.
An embodiment is contemplated in which the molding pockets are formed by orifices through at least a portion of the molding member. In one embodiment the molding member comprises a first band having orifices therethrough, and a second band, wherein a portion of the first band is in a contacting face-to-face relationship with a portion of the second band. When the flowable resinous material is deposited onto or into such a molding member, the flowable resinous material is disposed within the orifices of the first band and may be supported by the second band. Then, at a certain point in the process the first and second bands separate such that preferably only the first band is juxtaposed with the reinforcing structure.
The preferred flowable resinous material comprises a material selected from the group consisting of epoxies, silicones, urethanes, polystyrenes, polyolefins, polysulfides, nylons, butadienes, photopolymers, and any combination thereof. The flowable resinous material is preferably supplied and deposited onto or into the molding member in a liquid form. The surface energy of the molding surface in contact with the resinous material is preferably lower than the surface energy of the reinforcing structure. Prior to depositing the resinous material onto or into the molding member, the molding surface of the molding member may be treated with a release agent to lower the surface energy of the molding surface.
In the preferred continuous process a further step is required of continuously moving the molding member and the reinforcing structure at a transport velocity such that at least a portion of the reinforcing structure is in a face-to-face relationship with at least a portion of the molding member. Preferably, the reinforcing structure contacts the molding member. The reinforcing structure and/or the molding surface may be supported by a support roll or an endless support band. The support roll is preferably juxtaposed with the molding member to form a nip therebetween. The support band is preferably juxtaposed with the molding member and is structured to move in a contacting face-to-face relationship with at least a portion of the reinforcing structure and/or the molding member. The preferred apparatus of the present invention has a machine direction, and comprises a means for moving the reinforcing structure and the molding member, and preferably a means for moving the support roll or band, in the machine direction such that a portion of the reinforcing structure is in a face-to-face, and preferably contacting, relationship with a portion of the molding member. The apparatus may have optional means for pressing the reinforcing structure and the molding surface relative to each other for a predetermined period of time.
A means for creating a fluid pressure differential may include any means known in the art, for example a vacuum apparatus. The fluid pressure differential should be sufficient to transfer the flowable resinous material from the molding member to the reinforcing structure.
Preferably, the process includes a step of controlling a caliper of the belt being constructed, and more specifically a thickness of the resinous material joined to the reinforcing structure, to at least one pre-selected value. The thickness of the resinous material may be controlled by a caliper-controlling device, including but not limited to a pair of juxtaposed rolls forming a clearance therebetween, or any other means known in the art, such as, for example, a laser beam, a knife, etc.
Preferably, the flowable resinous material is transferred from the molding member to the reinforcing structure substantially in a pre-selected pattern. Depending on the desired pattern of the resinous framework of the belt being constructed, the resinous material may be transferred to the reinforcing structure in a substantially continuous pattern, in a pattern comprising a plurality of discrete protuberances, or in a semi-continuous pattern. Preferably, the resinous material extends outwardly from the first side of the reinforcing structure after the resinous material has been joined to the reinforcing structure.
The reinforcing structure may comprise a variety of forms. One preferred reinforcing structure comprises a woven fabric or a screen having a plurality of open areas therethrough. Another preferred reinforcing structure comprises a felt. The reinforcing structure comprising a combination of the woven fabric and the felt is also contemplated.